Our Brain Uses a Not-So-Instant Replay to Make Decisions

From Scientific American (June 27):

The hippocampus is a small curl of brain, which nests beneath each temple. It plays a crucial role in memory formation, taking our experiences and interactions and setting them in proverbial stone by creating new connections among neurons.

A report published on June 27 in Science reveals how the hippocampus learns and hard wires certain experiences into memory. The authors show that following a particular behavior, the hippocampus replays that behavior repeatedly until it is internalized. They also report on how the hippocampus tracks our brain’s decision-making centers to remember our past choices.

Previous research has shown that the rodent hippocampus replays or revisits past experiences during sleep or periods of rest. While a rat navigates a maze, for example, so-called place cells are activated and help the animal track its position. Following their journey through the maze, those same cells are reactivated in the exact same pattern. What previously happened is mentally replayed again.

The authors of the new study were curious whether this phenomenon only applies to previous encounters with a particular location or if perhaps this hippocampal replay also applies to memory more generally, including mental and nonspatial memories.

It turns out it does.

In the study, 33 participants were presented with a series of images containing both a face and a house. They had to judge the age of either one or the other. If during the second trial, the age of the selected option remained the same, the judged category also did not change in the subsequent trial. If the ages differed, the judged category flipped to the other option in the next round. [read more]